EXPERIMENTS ON BLOOD VESSELS: (1) Electron microscopic study of the effect of electrically-induced spasm on small and medium-sized arteries. (2) Electron microscopic study of arterial endothelium after infusion of vasoactive drugs, including vasoactive amines. (3) Light and electron microscopic study of the arterial wall after experimentally-induced interstitial hemorrhage. (4) Light and electron microscopic study of the rat carotid artery after transient or permanent occlusion. (5) Histochemical and electron microscopic study of the periarterial and perivenous "veil cells". (6) Light and electron microscopic study of the aging aorta, in the rat and, if possible, in other animals. EXPERIMENTS ON THE MYOCARDIUM: (1) Light and electron microscopic study of the effect of massive pulmonary embolism or of pulmonary stenosis on the myocardium of the right ventricle (rat and dog). (2) Light and electron microscopic study of the "wavy fibers" in myocardial infarcts produced in the dog, at varying stages of the ischemic injury.